Preparation of calcium carbide



PREPARATION OF CALCIUIVI CARBIDE Willem van Loon, Geleen, and SiedsKoopal, Sittard, Netherlands, assignors to Stamicarhon N. V., Heerlen,Netherlands No Drawing. Application December 28, 1053,

Serial No. 400,768

Ciaims priority, application Netheriands December 30, 1952 6 Claims.(Cl. 23-208) The invention relates to the preparation of calcium carbidein shaft furnaces.

In this type of carbide manufacture, charges consisting of a mixture ofa solid fuel containing substantial amounts of carbon, such as coke,coal and charcoal, and a calcareous material such as unslaked lime,limestone and dolomite are fed into the top of the furnace, while theheat and high temperature required for the carbide formation areobtained by oxidizing and converting part of the fuel to gaseousmaterials with the aid of an oxygencontaining blast. The inflammablegases thus formed escape from the top of the furnace, while in the lowersection of the furnace a carbide melt is formed which can be dischargedcontinuously or periodically.

The blast used to obtain this result may consist for instance of oxygenenriched air, technical oxygen, pure oxygen or of a mixture of oxygenwith either steam or carbon dioxide.

The conversion of solid fuels mainly consisting of carbon by means of anoxygen-containing blast into inflammable gases, in the course of whichthe ashes of the coal are obtained in the form of a liquid slag, i awell-known process. In this process the composition of the blast isalways so selected that the temperature of the combustion zone will bein the range of about 1000 to 1800 C., which will result in exhaust gastemperatures of about 450 to 900 C. being obtained.

However, the temperature of the combustion zone required in themanufacture of calcium carbide is much higher, namely about 2000 to3000" C. Accordingly, it is to be expected that this very highcombustion zone temperature will be accompanied by high exhaust gastemperatures. In order to prevent considerable losses of heat assensible heat from the gas produced in the combined manufacture of gasand carbide in a shaft furnace it has previously been suggested to makeuse of regenerators.

OBJECTS It is an object of the present invention to prepare calciumcarbide by an improved method of reacting a calcareous material with asolid fuel source of carbon.

It is a further object to prepare calcium carbide in a shaft furnacewhile at the same time dispensing with the use of regenerators.

It is another object of this invention to prepare calcium carbide by amethod having a more favorable heat economy than prior art methods.

A further object of this invention is to obtain a more fluid melt thanthat obtained in prior art methods of forming calcium carbide in a shaftfurnace.

Another object is to obtain a calcium carbide yielding an increasedamount of acetylene upon hydrolysis.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter. It should be understood, however, that the detaileddescription and specific example, while indicating preferred embodiments2,794,706 Patented June 4, 1957 GENERAL DESCRIPTION These objects areaccomplished according to the present invention in the following manner.

Surprisingly we have found that the use of regenerators is entirelysuperfluous and very low exhaust gas temperatures of to 200 C. can beobtained if the weight ratio between CaO and C in the charge is madebetwen 1 to 4 and l to 2 and preferably about 2 to 5, notwithstandingthe fact that if a carbide of a predetermined calcium to carbon ratio isdesired the processing of highly calcareous charge normally requireshigher cornbustion zone temperatures than the processing of a chargewith a lower calcium content.

In addition to the advantage of the more favorable heat economy which wefound to be incidental to the addition of a relatively large proportionof lime, we have also discovered that during the manufacture of acarbide of a given quality, e. g., carbide containing 62% of CaCz, whenthe weight ratio betWeen'CaO and C in the charge was greater than 1 to4, a more fluid melt was obtained than when said ratio was smaller.

Furthermore, it was found that the weight ratio between calcium oxideand carbon in the charge should not be made greater than 1 to 2, becauseabove this limit difficulties are frequently encountered due to the factthat the combustion zone becomes slagged. This slagging cannot beprevented no matter how high the temperature of the combustion israised.

EXAMPLES A more complete understanding of this invention and theoperation thereof may be had by reference to the following examples.Example 1 operates in accordance with the present invention and Example2, for comparison shows a similar but prior art method of operation.

Example 1 A shaft furnace was fed in accordance with our invention witha charge consisting of a mixture of 80 kg. of coke and 55 kg. oflimestone. The coke had an ash content of 10% and the ratio of CaO to Cwas about 2 to 5. The height of the fuel bed was 4 meters. A blastcomposed of 77% technical oxygen and 23% steam was employed as thisparticular gas mixture was found to be particularly elfective inobtaining a good carbide. The initial furnace temperature rose fromabout 2500 C. to about 2650 C. The temperature of the escapinginflammable gas was C. The carbide obtained yielded 240 liters ofacetylene per kilogram when decomposed with water.

Example 2 This example illustrates the results obtained when operatingoutside the ranges of the present invention.

The shaft furnace was fed with a mixture of 80 kg. of the same coke and25 kg. of the same limestone as in Example 1. The ratio of CaO to C wasabout 1 to 5. The fuel bed had a height of 4 meters. The blast used wasa mixture of 65% technical oxygen and 35% steam as those proportionswere found best for obtaining a good carbide using the ratio of coke tolimestone of this example. The gases escaping from the shaft furnace hada temperature of 280 C. The carbide obtained yielded 220 liters ofacetylene per kilogram when decomposed with water under identicalconditions with those employed in Example 1.

CONCLUSION The present invention provides a process for the manufactureof calcium carbide in a shaft furnace by starting from a mixture 'of "asolid fuel, mainly consisting of carbon, and a calcareous additioninwhichprocess part of the fuel present is converted to gases by anoxygencontaining gas in order to'provid'e the amount of heat and thehigh temperaturerequired forthe formation of calcium carbide, and aninflammable gas escapes through the top of the furnace, while in thelower section of the furnace molten carbide is collected which can bedischarged either continuously or periodically; the process according tothe invention being characterized by the fact that the weight ratio ofcalcium oxide and carbon in the charges to be supplied to the furnace ishigher than 1 to 4 and lower than 1 to 2.

A comparison of Example 1 with Example 2 shows that by operating inaccordance 'with the present invention it is possible to prepare calciumcarbide in a shaft furnace in which the gases escaping from the furnacehave a considerably lower temperature than the gases obtained when usinga lesser amount of calcium oxide while at the same time the process ofthe present invention results in a carbide having a greater yield ofacetylene per unit weight of the carbide.

We claim:

1. A process of preparing calcium carbide in a furnace from a mixture ofa solid fuel comprising carbon, and a calcareous material, said processcomprising converting part of said fuel to gases with anoxygen-containing blast in order to provide the heat and hightemperature required for the carbide formation, permitting theinflammable gas to escape through the top of the furnace, while in thelower section of the furnace molten carbide produced by the reaction ofthe remainder of said fuel and calcareous material is collected, theweight ratio between the calcium oxide and carbon in the calcareousmaterial and fuel mixture fed into the furnace being greater than about1 to 4 and lower than about 1 to 2.

2. The process of claim 1, wherein the solid fuel is a member of thegroup consisting of coke, coal and charcoal. a

3. The process of claim 1, wherein the calcareous material is a memberof the group consisting of unslaked lime, limestone and dolomite.

4. The process of claim 1, wherein the solid fuel is a member of thegroup consisting of coke, coal and charcoal, and the calcareous materialis a member of the group consisting of unslaked lime, limestone anddolomite.

5. A process of preparing calcium carbide in a furnace from a mixture ofa solid fuel selected from the group consisting of coke, coal andcharcoal and a calcareous material selected from the group consisting ofunslaked lime, limestone and dolomite, said process comprisingconverting part of said fuel to gases with an oxygen-containing blast ata temperature of about 2000 to 3000 C., permitting the inflammable gasto escape at a-temp'erature of about to 200 C. through the top of thefurnace, while in the lower section of the furnace molten carbideproduced by the reaction of the remainder of said fuel and calcareousmaterial is collected, the said ratio be tween the calcium oxide andcarbon in the calcareous material and fuel mixture fed through thefurnace being greater than about 1 to 4 and lower than about 1 to 2.

6. The process of claim 5, wherein the fuel is converted to gases at atemperature of about 2500 C. and the inflammable gas escapes at atemperature of about 180 C. and the ratio of calcium oxide to carbon isabout 2 to 5.

References Cited in the file of this patent UNITED STATES PATENTS1,374,317 Norton Apr. '12, 1921 1,507,740 Kirby Sept. 9, 1924 1,872,202Williams Aug. 16, 1932 2,380,008 Abrams July 10, 1945 FOREIGN PATENTS501,376 Canada Apr. 13, 1954

5. A PROCESS OF PREPARING CALCIUM CARBIDE IN A FURNACE FROM A MIXTURE OFA SOLID FUEL SELECTED FROM THE GROUP CONSISTING OF COKE, COAL ANDCHARCOAL AND A CALCAREOUS MATERIAL SELECTED FROM THE GROUP CONISTING OFUNSLAKED LIME, LIMESTONE AND DOLOMITE, SAID PROCESS COMPRISINGCONVERTING PART OF SAID FUEL TO GASES WITH AN OXYGEN-CONTAINING BLAST ATA TEMPERATURE OF ABOUT 200 TO 300*C., PERMITTING THE INFLAMMABLE GAS TOESCAPE AT A TEMPERATURE OF ABOUT 80 TO 200*C. THROUGH THE TOP OF THEFURNACE, WHILE IN THE LOWER SECTION OF THE FURNACE MOLTEN CARBIDEPRODUCED BY THE REACTION OF THE REMAINDER OF SAID FUEL AND CALCAROUSMATERIAL IS COLLECTED, THE SAID RATIO BETWEEN THE CALCIUM OXIDE ANDCARBON IN TEH CALCAREOUS MATERIAL AND FUEL MIXTURE FED THROUGH THEFURNACE BEING GREATER THAN ABOUT 1 TO 4 AND LOWER THAN ABOUT 1 TO 2.